1. Field of the Invention
The present invention relates to a method and an apparatus for producing a semiconductor device having a heat-sinking plate as well as a semiconductor chip which is encapsulated with a plastic material.
2. Description of the Prior Art
FIG. 4 is a cross sectional view of a conventional semiconductor device having a heat-sinking plate. In this figure, leadframe 2 has a die pad 2a on which a semiconductor chip 1 is attached, inner leads 2b extending into a plastic package material 4 and outer leads 2c extending to the outside from the plastic package material 4. Here, an inner lead 2b and an outer lead 2c form one continuous lead. Inner leads 2b are connected to pads (not shown in the figure) on the chip 1 with fine metal wires 3. The semiconductor chip 1, fine metal wires 3, the die pad 2a, inner leads 2b and the heat-sinking plate 16 are encapsulated into one body with a plastic package material 4.
FIG. 5 is a exploded perspective view for explanation of a conventional method of producing a semiconductor device. In this figure, a mold 11 comprises a lower mold 12 and an upper mold 13. The lower mold 12 has a cavity 12a and positioning pins 12b in each of three corners. Each of these positioning pins 12b is inserted into a respective hole in supporters 16a of the heat-sinking plate 16 so that the heat-sinking plate 16 is correctly positioned. The upper mold 13 has a cavity 13a and three receiving holes. When the upper mold 13 and the lower mold 12 are together the cavities 12a and 13b form a space in which a leadframe 2 with a chip 1 mounted on it and a heat-sinking plate 16 are put. Plastic resin is injected into this space. The receiving holes 13b in the upper mold 13 receive the positioning pins 12b when the molds are clamped together. The heat-sinking plate 16 has pre-bent portions 16b so that there is a gap between the heat-sinking plate 16 and the leadframe 2.
Referring to the figure, a conventional method for manufacturing semiconductor devices is described next. In the first step, a semiconductor chip 1 is attached on a die pad 2a of a leadframe 2. Then pads (not shown in the figure) on the chip 1 are connected to inner leads 2b of the leadframe 2 with fine metal wires 3. The positioning pins 12b are inserted into the holes in the supporters 16a so that the heat-sinking plate 16 is fixed on the lower mold 12 at the correct position. After the leadframe 2 is put on the heat-sinking plate 16, the upper mold 13 and the lower mold 12 are clamped together. Then plastic resin (not shown in the figure) is injected into the space in which the leadframe 2 and the heat-sinking plate 16 are put. Thus the leadframe with a chip and the heat-sinking plate are encapsulated with plastic resin. Next, unnecessary portions of the leadframe 2 and of the heat-sinking plate 16 are cut away. Finally, the outer lead 2c is formed into a proper shape to produce the completed semiconductor devices shown in FIG. 4.
In the conventional method for manufacturing semiconductor devices having a structure as described above, each heat-sinking plate is put on the lower mold one individually in a troublesome positioning process which results in poor productivity. Moreover, because the heat-sinking plate is bent partly, handling it at bent portions 16b causes further unnecessary bending at the portion 16a affecting positioning. This results in the error in positioning of the heat-sinking plate.